1. Field of the Invention
The present invention relates to ink-jet printers and, more particularly to a cap for a service station for servicing ink-jet printheads.
2. Description of the Related Art
Ink-jet printers print by shooting drops of ink onto a page. The ink is stored in a reservoir and discharged onto the page through nozzles in a printhead. To print an image, the printhead moves back and forth across the page shooting drops as it moves.
A problem with ink-jet printers is that air bubbles may be forced into the nozzles to interfere with the operation of the printhead. Additionally, ink may drool out of the nozzles, dry and clog them. Debris such as dirt and paper dust may also collect on the printhead and clog the nozzles.
To address these problems, ink-jet printers typically include caps and service stations. A cap encloses and defines a cavity around the printhead when the printhead is not in use or needs servicing. A service station is a location on the printer where the printhead can be serviced. The cap is usually located in the service station.
The cap helps prevent ink from drying on the printhead by providing a cavity that is kept moist. Ink is discharged into the cavity and the moisture from the ink keeps it from drying on the printhead.
However, the volume of the cavity is decreased when the cap encloses the printhead, resulting in a change of pressure within the cavity. If the pressure within the cavity changes, air bubbles are forced into the nozzles of the printhead. Thus, the caps are vented to allow the pressure within the cavity to equalize with the pressure outside the cavity so that air bubbles are not forced into the nozzle of the printhead.
Previously, caps have been vented through a pump connected to the cavity. An example of such a cap is disclosed in U.S. Pat. No. 4,853,717 entitled "Service Station for Ink-Jet Printer."
When an ink-jet printer is turned on, a control algorithm causes the printhead to fire ink through all the nozzles into the cap to clean the nozzles and remove any plugs of ink. The nozzles may also be fired at selected times during printing. The drops of ink that are fired keep the cavity defined by the cap moist or in a humid environment so that ink will not dry on the printhead when it is not in use.
Commonly, an elastic cap is placed over the nozzle end of a printhead to ensure a sufficiently humid environment. Such a cap must form a leak-free seal between the printhead nozzles and the ambient environment. Forcing the cap onto the printhead with enough force to deform the cap around its sealing lip accomplishes this leak-free seal. An example of such an elastic cap is disclosed in U.S. Pat. No. 5,448,270 entitled "Ink-Jet Printhead Cap Having Suspended Lip."
A problem with ink-jet printhead caps is that the humid environment within a cavity around the nozzles may be comprised through vents that open directly to the cavity.
To address this problem, the vents may be covered with an absorbent pad to create an effective seal while insuring venting to the ambient environment, thereby preventing the cavity from being dried.
An object of the present invention is to provide an effective seal between the cavity defined by a cap and the ambient environment without any absorbent pad.